We've been considering getting chickens. When I say considering I mean obsessively researching and trying to read every single book and website written on the subject.
After learning that a local friend discovered high levels of lead in her soil, I started looking into that aspect too. We too live in an urban (well, suburban) area that could potentially be contaminated. See the NYTimes article High Lead Found in City-Sourced Eggs for more info.
In our case, the ideal chicken run area is right next to a small playhouse that was built in 1955. The playhouse itself is what we'd be converting to a coop:
Being built in 1955 could mean that at one time it was painted with lead paint and then scraped off...and then the soil would be contaminated. Additionally, we live in an area that was once covered with citrus groves where lead arsenate may have been used as a pesticide. I braced myself for the worst.
Fortunately, our soil test results were fine.
Anything less than 22ppm is considered low and ours was only 1.7. Huge relief.
We had our soil tested from UMass Soil Testing and it was only ten bucks! We took samples per their instructions and mailed it off in a ziplock. A week later they emailed the results.
So we got the green light.
Now we just need chickens.
Actually, it isn't quite that simple. Now we're chicken converting the playhouse coop, predator-proofing it obsessively, adding ventilation, building a large run, building nesting boxes, researching and getting food and other supplies... wow LOTS to do.